Java Object Migration

I have a application (Java 1.4 Compiled) that would cache the object in a DB and access it constantly during the activity of the application, now the application is recompiled with the JDK 1.5 version and currently we are stuck with a problem of the Object cache facing the class mismatch / Serialization exception since the object cache created for the Java 1.4 is not compatible with the JDK 1.5 complied classes. I cannot remove these cache directly since it is specific to individual users and has a definite values that has to be re-used.

please advice if there exist any possibility of migrating these objects directly from 1.4 to 1.5 .